1. Field of the Invention
This invention relates to charge coupled device, (CCD) and more particularly to an interface which permits charge to flow between BCCD and SCCDs.
2. Description of the Prior Art
Buried channel CCD (BCCD) and surface CCD (SCCD) structures each have unique characteristics that can make one more suitable than the other for a given device application. For example, the BCCD can operate at higher speeds and has a higher transfer efficiency, whereas the SCCD has a better charge-carrying capacity, is easier to build, has greater linearity in its input, and generally exhibits less leakage current. Historically, CCD devices have been fabricated either entirely as buried channel or entirely as surface channel; however, one can conceive of device structures which could benefit from the inclusion of both types of CCDs. For example, if a series-parallel-serial (SPS) array were needed for an application that required high speed and large charge-carrying capacity, one solution would be to make the input and output register a BCCD and the parallel section a SCCD. The difficulty that arises when a buried channel and a surface channel are combined in the same circuit is that an interface must be designed between the two channels that will overcome the potential barrier created by a buried to surface channel transfer thereby allowing charge to flow between them. This barrier is attributable to the use of opposite semiconductor types in the buried and surface channel regions, i.e., p-doped and n-doped materials. The purpose of the present invention is to permit the charge to flow between the buried channel and surface channel.